1. Field of the Invention
The invention relates to a system and a method for controlling a power transmission apparatus for a vehicle, which includes a first shift portion that is able to function as an electric differential portion, and a second shift portion that is a stepped shift portion, and that is connected to the first shift portion. More specifically, the invention relates to improvement for reducing the possibility that a driver feels that drive power is not quickly increased, and the drive power is insufficient when the driver depresses an accelerator pedal.
2. Description of the Related Art
A power transmission apparatus, which includes a first shift portion and a second shift portion connected to the first shift portion, and which transmits power output from the engine to drive wheels, is available. The first shift portion includes a motor and a differential portion, and is able to function as an electric differential portion. The second shift portion is a stepped shift portion. For example, Japanese Patent Application Publication No. 2005-319924. (JP-A-2005-319924) describes a control device for a drive apparatus for a vehicle. The drive apparatus for a vehicle in the technology includes a first shift portion that is able to function as an electric continuously variable transmission, and a second shift portion in which any one of a plurality of gears is achieved. The first shift portion is connected to the second shift portion in series. The mode of the first shift portion is selectively switched between a CVT mode in which electric CVT operation is performed, and a stepped transmission mode in which the CVT operation is not performed. The control device separately controls the speed ratio of the first shift portion, and the speed ratio of the second shift portion. In addition, the control device changes, in a stepwise manner, the speed ratio (total speed ratio) of an entire transmission constituted by the first shift portion and the second shift portion. Also, the drive apparatus for a vehicle selectively switches the drive mode of a vehicle among an engine-drive mode in which an engine is solely used as a drive power source, an engine-and-motor-drive mode in which the engine and a motor are used as the drive power sources, and a motor-drive mode in which the motor is solely used as the drive power source.
However, in the above-described control in the related art, when it is determined that the engine should be started based on depression of an accelerator pedal after an upshift is started while the vehicle is driven in the motor-drive mode using solely the motor as the drive power source, the start of the engine is delayed until the upshift is completed. Therefore, drive power corresponding to the depression of the accelerator pedal may not be quickly output, and accordingly, a driver may feel that the drive power is not quickly increased, and the drive power is insufficient.